The present invention relates generally to gas turbine engines, and, more specifically, to variable stator vane actuation in multi-stage axial compressors thereof.
In a gas turbine engine, air is pressurized in a compressor and channeled to a combustor wherein it is mixed with fuel and ignited for generating hot combustion gases which flow downstream therefrom into one or more turbine stages which extract energy therefrom for powering the compressor and producing useful work. A typical compressor has a plurality of axial stages which compress the air in turn as it flows downstream. And, each compressor stage includes a row of rotor blades extending radially outwardly from a compressor spool or disk, and a cooperating row of stator vanes extending radially inwardly from an annular casing.
In order to control performance and stall margin of the compressor, many of the stator vane rows are variable for selectively adjusting the angle of the vanes relative to the air being compressed. Variable stator vanes include a spindle which extends radially outwardly through a casing and to which is attached a lever. The lever in turn is pivotally joined to a unison ring coaxially surrounding the compressor casing. The several unison rings for the different variable stages are in turn typically joined to a common beam pivotally joined to the casing at one end and joined to a suitable actuator at an opposite end. The actuator pivots the beam which in turn rotates the unison rings connected thereto which in turn rotates the respective levers attached thereto for pivoting the corresponding stator vanes.
Since the individual levers are pivotally joined to the unison rings, the unison rings are allowed to rotate circumferentially and translate axially to follow the path of the levers. The rotation of the unison rings directly rotates the attached levers and vanes in a substantially linear cooperation. And, the amount of stator vane pivoting varies from stage to stage since the several unison rings are joined to the common beam at correspondingly different pivoting lengths from the pivoting end of the beam.
Since a gas turbine engine typically operates over a range of output power, the operation of the compressor is correspondingly scheduled for maximizing efficiency of operation without undergoing undesirable aerodynamic stall. Vane scheduling is controlled by the kinematic motion of the levers, unison rings, and actuation beam.
However, it is desirable to introduce further variability in the stator vane position schedule for further improving engine performance and efficiency while maintaining an effective stall margin.